Effect Of Thermal Aging On Microstructure And Mechanical Properties Of Sanicro25/P92 Dissimilar Steel Welded Joints

Welded dissimilar steel can take full advantage of the excellent properties of various materials and is widely used in petrochemical,aerospace,power plant boiler and other industries.However,the dissimilar steel welded joints is easy to undergo tissue evolution and element migration in the process of long-term high temperature service,which then leads to the high temperature fracture of the welding joint.In this paper,Sanicro25/P92 was welded by tungstun-inert-gas(TIG)arc welding.After welding,the welded joint was placed in a high-temperature isothermal long-term thermal aging furnace to study the effect of thermal aging on the microstructure development,element migration and mechanical properties of the welded joint.1、According to the study of the microstructure of Sanicro25 / P92 welded joints,it is found that the tissue of P92 is divided into thermal influence area of P92 steel and non-thermal influence area of P92 steel.After aging,the grain size in the structure increases,the number of laver phase increases,and the laver Laves is mainly distributed at the grain boundary.The structure of P92 steel is divided into P92 steel heat-affected zone and P92 steel non-heat-affected zone.With the increase of particle size after aging,the number of lamellar phase,lamellar phase and crystal mainly distributed on the grain boundary increases.In the welding department of P92 steel coarse crystal heat affected zone observed δ ferrite,after aging δ ferrite number gradually increased to form δ ferrite zone.The microstructure of Sanicro25 steel and weld seam is austenitic grain and dendritic structure,respectively.The microstructure of Sanicro25 steel has no significant change after thermal aging,and the dendritic structure in the weld seam is coarsened.2、Through the analysis of element migration in Sanicro25 / P92 steel welded joints,a large concentration gradient was found between the matrix material and the weld on both sides of the dissolution line.After thermal aging,elements diffuse from the high concentration side to the low concentration side through the dissolution line,and the diffusion mode is "downhill diffusion".The carbon element in the heat affected zone of P92 steel weldment is mainly distributed at the grain boundary,and the carbon element in the grain is less.With the extension of thermal aging time,the carbon element in the grain gradually converges to the grain boundary and Laves direction.3、Through the study of the mechanical properties of welded joints of Sanicro25/ P92 steels,it is found that the hardness values at different locations in the weld section are different,with higher hardness values for Sanicro25 steel base material and weld seam,and slightly higher hardness values after thermal aging for 2000 h.The hardness values of P92 steel are relatively low and show a substantial decrease after thermal aging,among them,P92 HAZ steel has the minimum hardness of 191 HV,which is the weakest area of the whole welding section.Found in the organization the number of δ ferrite increases..After aging was the main reason for the significant decrease in the hardness value of P92 steel HAZ.Thermal aging reduces the strain and fracture time of creep,and both thermal aging reduces the plasticity and service life of welded joints.